The present invention relates to a pneumatic tire improved in wet performance, noise performance and steering stability.
In the laid-open Japanese Patent Applications JP-A-6-127215 and 7-276915, a pneumatic tire capable of improving wet performance and noise performance are disclosed, wherein, as shown in FIG. 14, the tread portion (t) is axially divided into a central part (e) and two shoulder parts (b) by two wide circumferential grooves (g). The central part (e) has a round profile extending from the bottom of one of the circumferential grooves to the bottom of the other. By contrast, each shoulder part (b) has a relatively edged corner between the top face and axially inner side face.
In such a pneumatic tire having wide circumferential grooves, the ground contacting area is inevitably decreased, and thereby it becomes difficult to satisfy requirements for the recent high performance cars, such as road grip performance in dry conditions, steering stability during cornering, initial steering response at the time of starting cornering, especially under high speed conditions.
It is therefore, an object of the present invention to provide a pneumatic tire which is improved in the road grip performance, steering stability, steering response and the like without sacrificing excellent wet performance and noise performance of wide circumferential grooves.
According to the present invention, a pneumatic tire comprises
a tread portion,
two wide circumferential grooves dividing the tread portion into a pair of shoulder parts and a central part therebetween, each of the circumferential grooves having a groove bottom having an axially inner edge, an axially inner sidewall and an axially outer sidewall,
in a meridian section of the tire, the axially inner sidewall extending substantially straight from said axially inner edge to a ground contacting top surface (2a) of the central part and inclined axially inwards, and the axially outer sidewall comprising a convex part extending axially outwardly to a merge point at which the convex part merges into a ground contacting top surface of one of the shoulder parts,
in a foot print of the tire, each of the circumferential grooves having a maximum axial width of not less than 35 mm.
Therefore, when the tire load shifts towards the shoulder part during cornering, the convex part contacts with the ground to increase the ground contacting area, and the steering response, steering stability and the like can be improved. Further, the shoulder parts 10 are increased in the rigidity and the cornering force is increased, which also improve the steering stability.